Melt Esterification Polymerization

Polycarbonates are manufactured via interfacial polymerization or through a melt esterification process. The properties of polycarbonate can differ greatly based on the method of polymerization. Specifically, the molecular weight distributions created by the two methods differ because of kinetic effects. Polycarbonates manufactured via interfacial polymerization tend to be less stable at high temperatures and less stiff than those produced via melt esterification, unless proper manufacturing precautions are taken. Therefore, when choosing a polycarbonate resin grade for a specific application, it is important to know the method by which it was produced. Either polymerization method can be performed as a continuous or batch process. 

What advantages does melt esterification have over interfacial polymerization in manufacturing polycarbonates ... 

The understanding of the SSP process is based on the mechanism of polyester synthesis. Polycondensation in the molten (melt) state (MPPC) is a chemical equilibrium reaction governed by classical kinetic and thermodynamic parameters. Rapid removal of volatile side products as well as the influence of temperature, time and catalysts are of essential importance. In the later stages of polycondensation, the increase in the degree of polymerization (DP) is restricted by the diffusion of volatile reaction products. Additionally, competing reactions such as inter- and intramolecular esterification and transesterification put a limit to the DP (Figure 5.1). 

PTT is melt polymerized by either the transesterification of PDO with dimethyl terephthalate (DMT) or by the direct esterification of PDO with purified tereph-thalic acid (PTA). The process is similar to that for PET but with major differences, as follows ... 

Because TPA has a melting point of >300 °C and poor solubility in PDO, direct esterification is preferably carried out in the presence of a heel under a pressure of 70-150kPa and at 250-270 °C for 100-140min. A heel is an oligomeric PTT melt with a degree of polymerization (DP) of 3 to 7, purposely left in the reaction vessel from a previous batch to improve TPA solubility and to serve as a reaction medium. The esterification step is self-catalyzed by TPA. 

A common method for polyester formation is via trans-esterification. The procedure described below uses a procedure that is modified from that described in Sorenson. In this case, aromatic di-acid 5 and di-ester 4 monomers are reacted together in the melt. During the polymerization, the molecular weight grows while volatile side-product is continuously removed from the reaction vessel by means of a vacuum pump. Scheme 2 describes the formation of a main-chain liquid crystalline poly(ester ether) containing... 

Polymer-bound Catalysts Various quaternary phosphonium salts are known to be excellent catalysts for trans-esterification and condensation polymerizations, e.g. melt polymerization of polycarbonates and polyesters. The ionomers from Exxpro elastomer can be used in those applications with added advantages such as solubility in the melt, ease of recovery and thermal stability. 

The product of the prepolymerization stage is continuously fed into the melt polymerization reactor, where the condensation reaction of the diol-ester to form the corresponding polyalkylene terephthalate (PAT) (either PET or PBT), shown in Figure 13.10. In this self-trans-esterification, the ester-diol is the source of both ester and alcohol functionalities. Since these PE products are semicrystalline, the reaction must be carried out above their melting point (r j) to prevent solidification of the... 

In melt polymerizations, the major part of the reaction is transesterification due to the fact that thermal pyrolysis nullifies much of the esterification of carboxyl end groups. A much larger percentage of the reaction in a solid state polymerization is esterification. The esterification involves residual carboxyl groups and hydroxyl groups. Another type of reaction is the addition of residual hydroxyl groups to vinyl ester groups. 

In direct melt polymerization, PBS is prepared using a two-step process. In the first step, esterification takes place at a temperature ranging from 150 to 200°C under atmospheric pressure or in a low vacuum, hi the second step, polycondensation is followed under a high vacuum at a higher temperature, e.g., 220-240°C, for... 

Solution polymerization of succinic acid and butanediol to PBS. Solution polymerization is a modified method of direct melt polymerization, which dissolves the raw materials in a solvent such as xylene or decahydronaphlhalene. The esterification reaction and the condensation reaction in the solvent improve the removal of the small molecular material formed in the reaction process, so the reaction can be conducted at lower temperature, which can avoid oxidation of PBS, but at the cost of a longer reaction time. 

Batch-melt (ester-interchanged, direct esterification), continuous polymerized, solid-phase polymerized and thin-film polymerized polymers samples where all analysed. 

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